1. Field of the Invention
The present invention relates to a lighting control apparatus for vehicle lamp, and relates particularly to a lighting control apparatus, for vehicle lamp, that controls the lighting of a semiconductor light source constituted by a semiconductor light emitting device.
2. Related Art
Conventionally, a halogen lamp or a discharge lamp is employed as a lighting source for vehicle lamps. If the light quantity is changed, the service life of a light source of this type may be greatly reduced, or the maintenance of a long lighting period may not be possible. Therefore, since the light is on by supplying a consistent amount of power, such as 55 W or 35 W, a consistent amount of power always is consumed.
On the other hand, when a semiconductor light emitting device, such as an LED (a Light Emitting Diode), is employed as a light source for vehicle lamp, the quantity of light emitted by the light source can be freely varied by changing the current that is supplied. Therefore, when an LED is employed as a light source for vehicle lamp, only the current supplied for the LED must be adjusted to obtain an adequate light quantity in consonance with the operating state. For example, when a vehicle is halted and the light quantity is reduced, the consumption of power is lowered, and energy can also be saved. Further, when a vehicle is traveling at less than a predetermined speed, or when the temperature of vehicle lamp exceeds a threshold value, heat generation by an LED can be suppressed by reducing the current supplied to the LED (see JP-A-2004-276737). In this case, when the current supplied to the LED is reduced, a light quantity of the LED, unlike a discharge lamp, can be reduced without a fade out failure occurring.
Unlike a halogen lamp or a discharge lamp, a semiconductor light source, such as an LED, has a low heat resistance. Thus, while taking the service life and the deterioration of a semiconductor light source into account, a dimming of a semiconductor light source can effectively be performed and can contribute to the prevention of a rise in temperature at the semiconductor light source.
However, when a semiconductor light source is dimmed, this is accompanied with a drastic change in the light quantity, even though power can be saved. Therefore, a driver may feel unconformable and partially blinded, and this will degrade driving safety.
The present invention is provided to resolve these conventional shortcomings. One objective of the invention is to ensure driving safety by regulating the quantity of light emitted by a semiconductor light source, and to, in the process, save energy.